Frequency measuring apparatus

ABSTRACT

This invention relates to a frequency measuring apparatus whereby a local oscillation frequency is determined by positively observing the higher harmonic number; superhigh frequencies ranging from several to several scores of gigahertzes can be precisely measured by using this higher harmonic number measuring apparatus.

United States Patent [191 11] 3,829,769 Ashida Aug. 13, 1974 [54] FREQUENCY MEASURING APPARATUS 3,087,121 4/1963 Bell 324/79 D [75] Inventor: Hitoshi Ashida y Japan 3,283,257 11/1966 Boyce 324/7) D [73] Assignee: Takeda Riken Industry Company Limited, Tokyo, Ja Primary Examiner-Alfred E. Smith Attorney, Agent, or Firm-William J. Daniel [22] Filed: Jan. 22, 1973 [21] Appl. No.2 325,582

[57] ABSTRACT [30] Foreign Application Priority Data Jan. 22, 1972 Ja an 47-8073 This invention relates to a frequency measuring apparatus whereby a local oscillation frequency is deter- [52] US. Cl 324/79 D mined by positively observing the higher harmonic [51] Int. Cl G01r 23/14 number; superhigh frequencies ranging from several [58] Field of Search 324/79 D, 79 R to several scores of gigahertz es can bc precis el y measured by using this higher harmonic number mea- [56] References Cited suring apparatus.

UNITED STATES PATENTS 2,539,673 l/l95l Peterson 324/79 D 4 Claims, 3 Drawing Figures VARIABLE FREQUENCY OSCILLATOR -TERMINAL FREQUENCY CONVERTER PHASE DETECTOR REFERENCE OSCILLATOR AUX. OSCILLATOR l. FREQUENCY CONVERTER PATENTEDAUG 1a 1914 3.829.769

FIGI

VARlABLE FREQUENCY FREQUENCY CONVERTER OSCILLATOR fl T-TERMINAL {COUNTER 0V PHASE DETECTOR I Ht Nh AUX. OSCILLATOR T B H REFERENCE OSCILLATOR L J FREQUENCY CONVERTER 5353E5Es INPUT **Hv Ho Hb T NB TERM'NAL OSCILLATOR COUNTER) VF OSCILLATOR Q OSClLLATORS PHASE .1 DETECTOR B H 4 Fl 6 2 REF. O'SCILLATOR FREQUENCY// Ht N v CONVERTERS v FREQUENCY F. CONVERTER (TUNER T --Hv C 7 NZ INPUT 1 TERMINAL COUNTER OSCILLATOR/'1 S -VOLTAGE GENERATOR w OSCILLATOR PHASE DETECTOR B H A Fl 6 3 REEosclLLAToR FRE COUNTER CON9 E IT0RS Hf Nh FREQUENCY MEASURING APPARATUS oscillatorl I-Iowever, a complicated apparatus has been required to determine such higher harmonic number and it has been difficult to positively determine the harmonic number.

provide a frequency measuring apparatus using a local oscillation frequency as described above, wherein the high harmonic number is positively observed witha simple device.

TriTfie drawings:

cording to the present invention.

Another objectof the present invention is to provide a simple apparatus for precisely measuring superhigh H5 delivers an output of the frequency A f i.e., the difference between the output frequency fs of the reference oscillator Os and the output frequency (fs l- A j) of the auxiliary oscillator t. Therefore, the counter Nh counts the number of the output frequency of the converter I-It for one period l/Af of this output or a time times (n is a positive or negative integer) as long as the period l/Af. Therefore, if the above mentioned counting time is, for example, 1/ Af, a counted 10 value d will be obtained. The output frequency dfs of frequencies ranging from several to several scores of 2 gigahertzs by using this higher harmonic number measuring apparatus. Particularly, a frequency measuring apparatus can be easily formed by adding a slight device to a spectrum analyzer.

FIGS. 1 to 3 are block diagrams showing various embodiments of the frequency measuring apparatus ac- FIG. 1 is a first embodiment of the present invention wherein the output of a voltage controlledtype variable frequency oscillator 0 and the output of a reference oscillator O such as a crystal oscillator, are applied to a phase difference detector B so that any higher harmonies of the output of the reference oscillator and the output of the variable frequency oscillator may be mixed together or each may sample the other. That is to say, when the output frequency of the variable frequency oscillator O coincides with the higher harmonics of the output of the reference oscillator 0 a direct current output will be sent out of the detector B. Therefore, by controlling the oscillator C with this direct current output, a phase synchronization is made between said oscillator O and the dth number higher harmonics of the reference oscillator 0 The apparatus in FIG. 1 is intended to measure the output frequency dfs of the oscillator 0 by determining the above mentioned higher harmonic number d in such case. The output is sent out of the output terminal T.

An auxiliary oscillator Ot having a slight or small fre quency difference Af between it and the reference oscillator O is provided, its output and the output of the variable frequency oscillator 0 are applied to a frequency converter Ht, the outputs of the reference oscillator O and auxiliary oscillator Ot are applied to a frequency converter l-Is and the output signal of the converter PM is applied to a counter Nh gated with the output of the converter Hs. That is to say, if the output frequency of the reference oscillator O and is fs, and the output frequency of the auxiliary oscillator Ot is (fs Af), an output of a frequency given by dA f will be sent out of the converter I-It by the mixing or sampling of the dth number higher harmonics of the output of this auxiliary oscillator and the output of the variable frequency oscillator Op. Further, the frequency converter the variable oscillator Op can be determined from this value d and the known output frequency fs of the referenceoscillator. Incidentally, it is evident that, in this case, if the maximum value of the anticipated higher 5 harmonic number d is D, the chance ofa mi sobservation can be eliminated by selecting the above mentione d slight frequency difference A f to be smaller than fs/ZD. The apparatus of the embodiment in FIG. 2 is in- 0 tended to count with a simple counter the frequency fx of the unknown signal to be measured applied to the terminal FfTlie s aTie parts a s in FIG. 1 are given corresponding designations inFIG. 2. As described above, the variable frequency oscillator Ov delivers the output of the frequency d f s. This output and the signal to be measured of the input terminal F are applied to the frequency converter Hv. Therefore, the converter Hv sends out an output of a frequency (fx dfs). This output and the known output of the oscilla- 0 tor 0a are applied to the frequency converter Ha. Therefore, if the output frequency of the oscillator 0a is fa, the converter I-Ia will send out an output of a frequency (fx dfs fa). Further, as this-output and the output of an oscillator 0b of a frequency jb are applied to a frequency converter Hb, this converter applies an output of a frequency (fx dfs fa fb) to the counter N]. The purpose of converters Ha and Hb with their associated oscillators is to bring the output frequency of converters Hv within the operating range of counter for if)" seconds (n is O or a positive or negative irie ger) and indicates its counted value. That is to say, if the counting time of the counter NI is I second, its counted value will be (fx dfs fa fb). Further, as the counter Nh indicates the higher harmonic number d, the frequency fx of the signal to be measured can be determined by the sum'of the value (dfs fa +jb), obtained by multiplying the value of said number d by the output frequency fs of the reference oscillator Os, and further d n t p tfreq sn e 12. andfb spe t el of the oscillators 0a and Ob and the counted value of the counter N1. Incidentally, if the output frequency of the reference oscillator Os is made, for example, 1 MHz, each of the units of the frequencies fa and jb is selected to be of 1 MHz ore more and these values are present at a unit of l MI-Iz in the counter Nh, the figures above 1 MHz will be indicate (T by 'connfefniiafi'a' the figures below MHz will be indicated by the counter NI. Therefore, the frequency of the signal to be measured can be directly read by arranging the indicating parts of the counters Nh and NI in series. Further, in the frequency converter I-Iv, it is possible to utilize the mth number higher harmonics of the output of the oscillator 0 In such case, the same measurement can be made by multiplying the counted value d of the counter Nh by m.

FIG. 3 is of an alternative embodiment for measuring the frequency of the unknown signal applied at the terminal F in which the output of a sweeping voltage gen- Nl. The counter Nl counts the frequency o f t h i s output erator S is applied'to the voltage controlled type variable frequency oscillator O in FIG. 1. That is to say, a sweeping oscillator is formed of the oscillator and voltage generator S. Where a measurement is made and the voltage generator S is started, the output frequency of the oscillator O will gradually increase or decrease. Accordingly, the output frequency of the frequency converter Hv will also vary and its output will be applied to a tuner C. Therefore, when the output frequency of the converter Hv coincides with the tuning frequency of the tuner C, an output will be sent out by the tuner and the output voltage variation of the sweeping voltage generator S will be stopped by that output signal. In this state, a phase synchronization is made between the variable oscillator O and the dth number higher harmonics of the output of the reference oscillator by the phase difference detector B and reference oscillator O in the same manner as in the apparatus in FIG. 2. Therefore, the frequency 'of the measured signal to be applied to the terminal F is determined by measuring the output frequency of the tuner C with the counter N1 and determining the higher harmonic number d with the counter Nh in the same way as in FIGS. 1 and 2. l

As explained with reference to the above embodiments, in the present invention, higher harmonic numbers can be positively measured with a simple apparatus. Further, by measuring superhigh frequencies by using this apparatus, there is an excellent effect'that frequencies can be precisely measured without requiring any costly counter high in the operating velocity and by only adding a slight device to the spectrum analyzer provided with a sweeping oscillator or the like.

What is claimed is:

l. A frequency measuring apparatus comprising:

a reference oscillator providing a reference frequency output,

a variable frequency oscillator providing a variable frequency output,

means for synchronizing said variable frequency output with the dth harmonic of said reference output,

an auxiliary oscillator providing an auxiliary frequency output differing slightly from the reference frequency output,

a frequency converter for receiving said auxiliary frequency output and said dth harmonic variable frequency output and giving an output equal to the dth harmonic of the frequency difference between said reference frequency and said auxiliary frequency, and

a counter for receiving said converter output and counting the frequency thereof divided by the slight difference in said reference and auxiliary frequencies whereby said counter indicates the harmonic number (I at which said variable frequency is synchronized. 2. The apparatus of claim 1 including a second fre- 5 quency converter for receiving the auxiliary frequency output and said reference frequency output and giving an output equal to the slight frequency difference therebetween and wherein said two converter outputs are gated by said counter whereby said counter counts l0 said first converter frequency output for a period proportional to the reciprocal of said frequency difference.

3. A frequency measuring apparatus comprising: a reference oscillator providing a reference frequency output, a variable frequency oscillator providing a variable frequency output, means for synchronizing said variable frequency output with the dth harmonic of said reference output,

an auxiliary oscillator providing an auxiliary frequency output differing slightly from the reference frequency output,

a frequency converter for receiving said auxiliary frequency output and said dth harmonic variable frequency output and giving an output equal to the dth harmonic of the frequency difference'between said reference frequency and said auxiliary frequency,

a counter for receiving said converter output and counting the frequency thereof divided by the slight difference between said reference and auxiliary frequencies whereby said counter indicates the harmonic number (I at which said variable frequency is synchronized,

a source of an unknown frequency signal to be determined, a further frequency converter for receiving the unknown frequency signal and the harmonic frequency output of said variable frequency and giving an output equal to the difference therebetween, and a further counter for counting said difference, whereby from the reference frequency and harmonic number indicated at said first counter, said unknown frequency can be calculated.

4. The apparatus of claim 1 wherein said variable oscillator is a sweeping oscillator and including a tuner receiving the output from said first frequency con- 50 verter, said tuner being operative to terminate the .sweep of said oscillator when output received thereby becomes substantially equal to a predetermined frequency.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,829,769

DATED August 13, 1974 INVENTOR(5) 1 Hitoshi ASHIDA It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, Claim 4, line 47, change 1" to 3 line 49, change "first" to further Signed and Scaled this second Day Of DecembeT 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissr'uner oj'Palenrs and Trademarks 

1. A frequency measuring apparatus comprising: a reference oscillator providing a reference frequency output, a variable frequency oscillator providing a variable frequency output, means for synchronizing said variable frequency output with the dth harmonic of said reference output, an auxiliary oscillator providing an auxiliary frequency output differing slightly from the reference frequency output, a frequency converter for receiving said auxiliary frequency output and said dth harmonic variable frequency output and giving an output equal to the dth harmonic of the frequency difference between said reference frequency and said auxiliary frequency, and a counter for receiving said converter output and counting the frequency thereof divided by the slight difference in said reference and auxiliary frequencies whereby said counter indicates the harmonic number d at which said variable frequency is synchronized.
 2. The apparatus of claim 1 including a second frequency converter for receiving the auxiliary frequency output and said reference frequency output and giving an output equal to the slight frequency difference therebetween and wherein said two converter outputs are gated by said counter whereby said counter counts said first converter frequency output for a period proportional to the reciprocal of said frequency difference.
 3. A frequency measuring apparatus comprising: a reference oscillator providing a reference frequency output, a variable frequency oscillator providing a variable frequency output, means for synchronizing said variable frequency output with the dth harmonic of said reference output, an auxiliary oscillator providing an auxiliary frequency output differing slIghtly from the reference frequency output, a frequency converter for receiving said auxiliary frequency output and said dth harmonic variable frequency output and giving an output equal to the dth harmonic of the frequency difference between said reference frequency and said auxiliary frequency, a counter for receiving said converter output and counting the frequency thereof divided by the slight difference between said reference and auxiliary frequencies whereby said counter indicates the harmonic number d at which said variable frequency is synchronized, a source of an unknown frequency signal to be determined, a further frequency converter for receiving the unknown frequency signal and the harmonic frequency output of said variable frequency and giving an output equal to the difference therebetween, and a further counter for counting said difference, whereby from the reference frequency and harmonic number indicated at said first counter, said unknown frequency can be calculated.
 4. The apparatus of claim 1 wherein said variable oscillator is a sweeping oscillator and including a tuner receiving the output from said first frequency converter, said tuner being operative to terminate the sweep of said oscillator when output received thereby becomes substantially equal to a predetermined frequency. 